This invention relates to improvements in an electroplating apparatus for particular use in automatically electroplating a number of relatively small sized workpieces.
As well known in the art of automatically electroplating such small workpieces, for example, as small screws, washers, watch parts, etc., it is essential to hold the small workpieces in good contact relation with the cathode surface during operation. In order to attain the aforesaid good contact, a method of utilizing centrifugal force was proposed with success to a certain degree, as disclosed in U.S. Pat. No. 3,359,195 (the same invention also disclosed in Japanese Pat. No. 504509), wherein a plating drum was arranged so as to rotate about its own axis to develop the centrifugal force. According to the method, however, such a disadvantage is observed that, in order to attain uniform electrodeposition on the overall surface of each workpiece and to prevent undesirable blind spot (non-plated small surface area) from occasionally occurring with some of the treated workpieces, it is necessary to reduce the rotational speed of the plating drum three or four times repeatedly per each performance, for the purpose of changing the contacting positions of the workpieces with the cathode surface, causing poor efficiency.
Thus, in order to eliminate the above-mentioned disadvantage, an improved method has been proposed as disclosed in U.S. Pat. No. 3,425,926 (the same invention also disclosed in U.K. Pat. No. 1,062,360, German Pat. No. 1,496,819 and Japanese Pat. No. 555787), wherein a plurality of plating drums or tanks are rotatably and eccentrically mounted on a rotatable table so that each drum or tank is rotatable about its own axis and an extraneous axis, whereby the desired uniform and blind-spotless electrodeposition can be obtained. However, the aforesaid improved method has another problem that it is structurally very difficult to design an efficient and economical electroplating apparatus equipped with a plurality of rotary drums or tanks capable of containing a sufficient quantity of plating solution. A simply large dimension of each of the drums will never solve the problem, because it causes not only poor efficiency in electrodeposition but also a considerable energy loss due to invited large electric resistance between electrodes. The large dimension of each drum also causes an inevitably enlarged size of the whole apparatus, which invites high costs in manufacture, maintenance and operation.
In the electroplating of small workpieces, large dimension of the plating drums is not advantageous as described above. On the other hand, in case the plating solution contained in the drum is so small in quantity, temperature thereof tends to easily rise up to an undesirable degree due to the heat from operative electric current between the electrodes as well as the heat from friction of the rotating parts of the apparatus, causing remarkable decrease in electroplating efficiency, as is well known in the art. Thus, according to the afore-mentioned prior art apparatus as disclosed in U.S. Pat. No. 3,425,926, it is necessary to discontinue the operation every two hours or so, to exchange the heated solution afresh for the purpose of preventing a rise of the solution temperature, which is apparently quite troublesome and inefficient. As for prevention of a rise of the solution temperature, one may easily think of a method by provision of a suitable cooling means, but it was practically very difficult to attach the cooling device to a rotary drum.
It is, therefore, the principal object of the present invention to eliminate the above-mentioned disadvantages in the prior art.
Another object of the invention is to provide an improved electroplating apparatus capable of minimizing an undesirable rise of solution temperature in order to maintain a good plating efficiency, thereby avoiding frequent interruptions in operation for the solution exchange.
A further object of the invention is to provide an improved type of electroplating apparatus which facilitates uniform electrodeposition on the entire surface of each of the small workpieces by means of one or more smaller rotary drums arranged within a larger drum so as to positively hold the workpieces in good contact relation with the cathode surface by the centrifugal forces developed when the smaller drums are orbitally revolved, as well as to agitate the workpieces for dislocation without losing the good contact with the cathode surface as each of the smaller drums is rotated on its own axis.
The above and other objects, features and advantages of the invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as definition of the limits of the present invention.